A variety of different types of blind are well known for covering architectural openings. Such blinds may be retracted and deployed across the architectural opening, for instance by means of lift cords. Also, it is known to tilt parallel components of the blind so as to change the appearance of the blind, for example moving between an open state and a closed state, particularly with blinds such as Venetian blinds.
It has been proposed previously to provide Venetian blinds with a double pitch configuration such that, in an open state, pairs of slats are located adjacent one another, leaving double pitch openings between the respective pairs. Arrangements have also been proposed whereby one set of slats can be moved separately from another set of slats, for example where alternate slats are part of one set or, alternatively, the slats of the top half of the blind are part of one set.
U.S. Pat. No. 5,119,868 describes a tilt assembly which is able to control upper and lower sets of Venetian blinds separately. The tilt assembly includes two rotatable drums for controlling respective tilt ladders. An axial spline gear is movable within and between the two drums by means of a horizontally movable control rod. Depending upon whether the inner spline gear is in one or other or both of the drums, it becomes possible to vary the tilt of the upper set of slats, the lower set of slats or both sets of slats.
EP 0 887 507 A2 also relates to a tilting mechanism for a Venetian blind where it is possible to control a top set of slats separately from a bottom set of slats. Tilt ladders for the respective sets are controlled by co axial drums in the tilt assembly. The two drums are rotatable together until they reach the end of an allowable rotation range. At that point, with one of the drums prevented from further rotation, a planetary gear mechanism causes the other drum to reverse its direction of rotation.
WO 2008/150789 describes three different arrangements for controlling two sets of slats. In the first arrangement, co axial drums are provided, in the second arrangement, parallel drums are provided and, in the third arrangement, co axial asymmetric flanges are provided. For the first arrangement, it is recognized that by attaching tilt ladders to the drums differently, it is possible to achieve a double pitch configuration, to tilt alternate slats in opposite directions or to tilt upper and lower sets of slats separately. The drums are driven by a co axial rotatable tilt rod which drives an elongate cylindrical drum driver. The drum driver has a protrusion which extends into a crescent-shaped opening within one of the drums such that the drum driver is able to move freely relative to the drum between the two ends of the opening and then drive rotation of that drum. A lash spring, formed as a coil spring, grips inner portions of the two drums such that they rotate together. By restricting rotation of the other drum, the force of the lash spring may be released so as to allow relative movement between the two drums.